1. Technical Field
The present invention relates to a flat display apparatus and an integrated circuit and can be applied to, for example, liquid crystal display apparatus in which drive circuitry is integrally formed on an insulating substrate. In the present invention, processing results from a circuit block on the side of a higher power supply voltage is inputted to the side of a lower power supply voltage through active elements performing on-off operation complementarily, and the output of these active elements is set to a predetermined level by the fall of the power supply voltage on the higher side thereof, which can further reduce power consumption in the deep-standby mode or the like.
2. Background Art
In recent years, in a liquid crystal display apparatus that is a flat display apparatus applied to a mobile terminal device such as a mobile telephone, for example, there has been provided the one in which a drive circuit of a liquid crystal display panel such as a horizontal drive circuit and a vertical drive circuit is combined and integrated on a glass substrate which is an insulating substrate making up the liquid crystal display panel.
More specifically, in this type of liquid crystal display apparatus, a display unit is formed by arranging, in a matrix, pixels each composed of a liquid crystal cell, a polysilicon TFT (Thin Film Transistor) which is a switching element of this liquid crystal cell and a storage capacitor. In the liquid crystal display apparatus, the respective pixels of the display unit formed in this manner are sequentially selected on a line basis by the driving of gate lines by the vertical drive circuit. Furthermore, gradation data indicating the gradation of the respect pixels is sampled sequentially and circularly by the horizontal drive circuit to be collected on a line basis, and by driving respective signal lines according to a digital-analog conversion result of this gradation data, the respective selected pixels are driven by the gate lines according to the gradation data, thereby displaying a desired image.
In such liquid crystal display apparatus, power supplies required for the operation are generated from power supplied externally, in a DC-DC converter, which is a part of the drive circuit provided in the vicinity of the display unit and the resultant power supplies of a plurality of systems enable the operation. Specifically, the apparatus is arranged such that, for example, a power supply of 6V and a power supply of −3V are generated from a power supply of 3V that is supplied externally, and these power supplies of −3V, 3V, and 6V enable the operation.
Thus, in this type of liquid crystal display apparatus, for example, as shown in FIG. 1, a 6 V-system logic electronic circuit 1 which is a circuit block whose power supply voltage is 6V allows various types of processing to be executed at high speed and according to the results of the high speed processing, a 3 V-system logic electronic circuit 2 which is a circuit block whose power supply voltage is 3V is driven.
In a mobile telephone which is one of devices to which this liquid crystal display apparatus is applied, for example, as disclosed in Japanese Application Publication No. 10-210116, stopping the display of the liquid crystal display unit in a standby state prevents wasteful consumption of battery.
Specifically, in the mobile telephone, a backlight of the liquid crystal display apparatus is turned off by the control of a controller that controls overall operation, which reduces power consumption. Furthermore, the operation mode of the liquid crystal display apparatus is set to be a so-called deep standby mode.
Here, the deep standby mode is, in the liquid crystal display apparatus, an operation mode in which, although the power is supplied externally, by stopping the supply of various clocks as operation references, the operation of the drive circuit is stopped.
More specifically, when the operation of the liquid crystal display apparatus is stopped in this manner, the simplest method is a method of stopping the supply of power to the liquid crystal display apparatus. However, when such stop of the supply of power is executed outside of the liquid crystal display apparatus, the configuration becomes complicated for that purpose in the mobile telephone. In contrast, while a method of shutting off the power supplied externally inside of the liquid crystal display apparatus is considered, in this case, the configuration of the active elements relating to the control of the power supply is increased in size, which brings an increase in size to the shape of the liquid crystal display apparatus itself.
Therefore, in this type of liquid crystal display apparatus, the deep standby mode is provided, in which the supply of clocks is stopped to stop the operation and to reduce the power consumption. Furthermore, in this deep standby mode, the operation of the DC-DC converter is switched so that the lowest power supply voltage in the liquid crystal display apparatus is outputted, which prevents through-currents between circuit blocks having different power supply voltages.
More specifically, FIG. 2 is a block diagram showing a configuration of a part of a digital-analog conversion circuit in this type of liquid crystal display apparatus. In this type of liquid crystal display apparatus, a predetermined generation reference voltage is resistively divided by resistances in a reference voltage generating circuit to generate a plurality of reference voltages. The plurality of reference voltages are selectively outputted according to the gradation data to thereby apply digital-analog conversion processing to the gradation data, and according to this digital-analog processing result, the respective pixels are driven. Furthermore, for example, in the case where the pixels are driven by line inversion, the polarity of this generation reference voltage is switched on a horizontal scanning cycle.
FIG. 2 is a diagram showing a circuit block relating to the switching of the polarity of the generation reference voltage and the generation of the reference voltages in such manners. In the liquid crystal display apparatus, various reference signals in sync with the gradation data are processed by a circuit block whose power supply voltage is 6V to thereby generate a polarity switching signal of the generated reference voltage and this polarity switching signal and an inversion signal of the polarity switching signal are outputted to a reference voltage generating circuit 5 via buffer circuits 3, 4 operating by the power supply voltage of 6V.
The reference voltage generating circuit 5 is a circuit block operating by a power supply voltage of 3V and by driving switch circuits 6 and 7 each composed of a CMOS (Complementary Metal Oxide Semiconductor) by the output signals of the buffer circuits 3, 4, contact points of the switch circuits 6 and 7 are switched complementarily to switch the polarity of the generated reference voltage to be outputted to a resistance block 8. Thus, in the example as shown in FIG. 2, the generated reference voltage is switched between +3V and −3V.
In the reference voltage generating circuit 5, the resistance block 8 is composed of a series circuit of a plurality of resistances and reference voltages V1 to V30 is generated by resistively dividing the generated reference voltage by this resistance block 8.
In such a configuration, when the operation of the DC-DC converter is simply stopped, the power supply voltage falls to 0V in the circuit block of the power supply voltage 6V, and as a result, the output of the buffer circuits 3, 4 is held in a state of falling to 0V. In this case, in the switch circuits 6, 7 receiving the output of these buffer circuits 3, 4, switch circuits 6A, 6B, 7A, 7B making up the respective switch circuits 6, 7 are held in an on-state, which causes through-currents 16, 17 in the switch circuits 6, 7.
In this case, also, for the circuit block of the power supply voltage 3V, by making the power supply fall, through-currents can be prevented. However, the fall of the power supply of the circuit block of the power supply 3V ends up shutting off the power supplied to the liquid crystal display apparatus itself, which causes problem such as an increase in size of the liquid crystal display apparatus as described above. Therefore, in this case, the switching of the operation of the DC-DC converter allows the power supply of 6V to fall to 3V in the liquid crystal display apparatus to prevent the through-currents.
However, even when the power supply of 6V is made to fall to 3V by the switching of the operation of the DC-DC converter in this manner, leak current by the power supply voltage 3V eventually continues to flow in each active element. If such leak current can be reduced, the power consumption can be further reduced in the deep standby mode.